This invention relates to the field of line width metrology, and more particularly, this invention relates to a method of determining errors in a line width metrology device.
Line width metrology devices, such as a scanning electron microscope, typically do not judge the quality of an output amplitude modulated signal with respect to instrumental error. The scanning electron microscope, produces a profile of the intensity versus position. Most of the information in the past has been taken from an arbitrary position on the waveform to produce the critical dimension of the line width. Most manufacturers have focused on the features that are analyzed, such as a photoresist feature, and not the intensity signal itself, to obtain information about the scanning electron microscope. For example, a problem may exist when the scanning electron microscope (or other metrology instrument) is not in focus and gives a different value of the critical dimension. An out of focus line width metrology device could widen the profile based on the arbitrary position that is picked for the critical dimension width. Thus, it would be advantageous if the critical dimension number was not focused on as in the prior art to determine the operating accuracy error in the scanning electron microscope or similar line width metrology device.
It is therefore an object of the present invention to provide a method of determining the accuracy error in scan signals of a semiconductor line width metrology device.
In accordance with the present invention, a method of determining the accuracy error in scan signals of a semiconductor line width metrology device, such as a scanning electron microscope, creates a frequency signature template of a patterned feature formed on a semiconductor layer with the line width metrology measurement device that is in nominal operating condition. A similar patterned feature formed on a semiconductor layer is scanned with the line width metrology measurement device for generating a waveform signal of the line width of the similar patterned feature. The waveform signal is processed to convert the signal into a frequency signature. The relative power of the frequency components of the frequency signatures are compared to the frequency signature template and the accuracy of the line width metrology device is determined based on the relative proportions between the frequency signatures of the similar patterned feature and template.
In still another aspect of the present invention, the method comprises the step of determining the relative proportions between the low and high frequencies of the frequency signature template and comparing the relative proportions of the low and high frequencies of the frequency signature template with the frequency signature obtained from the similar patterned feature. The relative proportions of high and low frequencies can be compared to the mid-range frequencies corresponding to the spacing. The high frequencies within the frequency signature template can be compared with high frequencies in the frequency signature obtained from the similar patterned feature. The step of scanning further comprises the step of generating an amplitude modulated waveform signal, such as produced from a scanning electron microscope or a semiconductor stylus measurement tool.